Relationship between thermal maturation gradients, geothermal gradients and estimates of the thickness of the eroded foreland section, southern Alberta Plains, Canada

Abstract

Analysis of post-Laramide (Tertiary) uplift and erosion in the southern Alberta Plains indicates that the greatest erosion occurred in regions where the youngest stratigraphic units are preserved. This is consistent with geological structure and the few preserved stratigraphic constraints on erosional history. Throughout this region, erosion is pervasive and the uplift history is commonly constrained by coalification data. The analysis of coalification, erosion and paleogeothermics are interrelated and knowledge of them is important to understand hydrocarbon generation and tectonic history. Several independent attempts to analyse coalification, erosion and paleogeothermics in this area have given different results. The most striking differences are those between estimates derived from the analysis of well profile coalification gradient and those determined using a commonly accepted relationship between the amount of eroded section and the equilibrium moisture content of near-surface coals. The match between present and paleogeothermal gradient fields is better when the latter technique is used. Correlation is expected between the late orogenic and present geothermal gradient fields because the hydrodynamically controlled advective heat flow pattern that now dominates geothermal gradients in the Mesozoic and Tertiary Foreland succession was initiated by the growth of topography in the west throughout Cordilleran orogeny. Well profile coalification gradients have significant, though commonly unacknowledged, uncertainties. These uncertainties are propagated in erosion and paleogeothermal gradient calculations. Ideally the relationship between erosion estimates using well profile coalification gradients and near surface coal properties can be compared. Unfortunately, the uncertainties in well profile coalification gradients prevent this.